Method and apparatus for providing fast reroute of a packet that may be forwarded on one of a plurality of equal cost multipath routes through a network

ABSTRACT

A method, apparatus and computer program product for providing fast reroute of a packet that may be forwarded on one of a plurality of Equal Cost Multi Path (ECMP) routes through a network is presented. A packet is received by a Forwarding Data Unit (FDU) in a data plane of a network element. The unicast packet is routed at L3, and ECMP is enabled for a next hop for the unicast packet. An ECMP route is selected for forwarding the packet to a destination port. A lookup is performed in a port state table maintained by the FDU to determine an available local port for said ECMP route that is in an UP state for the destination, and if no local port is UP, then a lookup is performed in the port state table to determine an available remote port that is in an UP state for the selected ECMP route.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of U.S. Provisional PatentApplication No. 61/178,014, filed on May 13, 2009, which is incorporatedherein by reference in its entirety. This application also relates tothe application titled “Method And Apparatus For Maintaining Port StateTables In A Forwarding Plane Of A Network Element”, Attorney DocketNumber AVA10-17, filed on the same date as the present application. Theteachings and disclosure of the above-identified applications are eachincorporated by reference herein in their entirety.

BACKGROUND

Data communication networks may include various computers, servers,nodes, routers, switches, hubs, proxies, and other devices coupled toand configured to pass data to one another. These devices are referredto herein as “network elements,” and may provide a variety of networkresources on a network. Data is communicated through data communicationnetworks by passing protocol data units (such as packets, cells, frames,or segments) between the network elements over communication links onthe network. A particular protocol data unit may be handled by multiplenetwork elements and cross multiple communication links as it travelsbetween its source and its destination over the network. Hosts such ascomputers, telephones, cellular telephones, Personal Digital Assistants,and other types of consumer electronics connect to and transmit/receivedata over the communication network and, hence, are users of thecommunication services offered by the communication network.

Network elements are typically implemented to have a control plane thatcontrols operation of the network element and a data plane that handlestraffic flowing through the network. The data plane typically will havea collection of line cards having ports that connect to links on thenetwork. Data is received at a particular port, switched within the dataplane, and output at one or more other ports onto other links on thenetwork. To enable the data to be handled quickly, the data plane istypically implemented in hardware so that all of the decisions as to howto handle the data are performed using hardware lookups, etc.

Ports can fail for many reasons, including line card failure, failure ofthe link connected to the port (e.g. line cut), far-end line cardfailure, etc. The terms multi-link trunk (MLT), Link Aggregation Group(LAG) and logical ports are synonymous and these terms are usedinterchangeably Likewise, the internal forwarding datapath within thenetwork element may fail which may cause a port or set of ports toappear to have failed, or there may be some other failures along thelogical/virtual connection to the port's external peer endpoint. Thereare numerous reasons why a port may fail.

In the event a port fails, traffic destined to the port should bediverted to flow out an alternate port to enable connectivity to berestored through the network. To minimize impact on the traffic beinghandled by the network element, e.g. to minimize down-time and packetloss, the quicker the rerouting of traffic can occur the better.Preferably, it would be advantageous to enable the traffic to fail overto an alternate port in under ten milliseconds (ms). Preferably, in thecase of LAG or MLT, the traffic should be spread across the remainingports rather than all moved from the failing port to a particulardesignated alternate port to prevent the designated alternate port frombeing overloaded with traffic.

SUMMARY

Conventional mechanisms such as those explained above suffer from avariety of deficiencies. One such deficiency is the amount of time takenby conventional network elements to recover from a failure. The longerthe amount of time taken to recover the longer the delay in performance(including more dropped packets) as well as the loading of other portsto overcome for the failed port.

Embodiments of the invention significantly overcome such deficienciesand provide mechanisms and techniques that provide a fast reroute of apacket that may be forwarded on one of a plurality of equal costmultipath routes through a network. In a particular embodiment of amethod for providing fast reroute of a packet that may be forwarded onone of a plurality of Equal Cost Multi Path (ECMP) routes through anetwork, the method includes receiving a packet by a Forwarding DataUnit (FDU) in a data plane of a network element, wherein the unicastpacket is routed at L3, and wherein ECMP is enabled for a next hop forthe unicast packet. The method also includes selecting an ECMP route forforwarding the packet to a destination port. The method further includesperforming a lookup in a port state table maintained by the FDU todetermine an available local port for said ECMP route that is in an UPstate for the destination, and if no local port is UP, then performing alookup in the port state table to determine an available remote portthat is in an UP state for the selected ECMP route. The methodadditionally includes wherein when no available port is determined forthe selected ECMP route, selecting another ECMP route if another ECMProute is available and repeating said performing the lookup in the portstate table until a port is found for the packet. Additionally themethod includes forwarding the packet to the available port using theselected ECMP route or dropping the packet when an ECMP route is notavailable.

Other embodiments include a computer readable medium having computerreadable code thereon for providing fast reroute of a packet that may beforwarded on one of a plurality of Equal Cost Multi Path (ECMP) routesthrough a network. The computer readable medium includes instructionsfor receiving a packet by a Forwarding Data Unit (FDU) in a data planeof a network element, wherein the unicast packet is routed at L3, andwherein ECMP is enabled for a next hop for the unicast packet. Thecomputer readable medium includes instructions for selecting an ECMProute for forwarding the packet to a destination port. The computereadable medium further includes instructions for performing a lookup ina port state table maintained by the FDU to determine an available localport for said ECMP route that is in an UP state for the destination, andif no local port is UP, then performing a lookup in the port state tableto determine an available remote port that is in an UP state for theselected ECMP route. The computer readable medium also includesinstructions wherein if no available port is determined for the selectedECMP route, selecting another ECMP route if another ECMP route isavailable and repeating said performing the lookup in the port statetable until a port is found for the packet. Additionally the computerreadable medium includes instructions for forwarding the packet to theavailable port using the selected ECMP route or dropping the packet whenan ECMP route is not available.

Still other embodiments include a computerized device (e.g., a networkelement), configured to process all the method operations disclosedherein as embodiments of the invention. In such embodiments, thecomputerized device includes a memory system, a processor,communications interface in an interconnection mechanism connectingthese components. The memory system is encoded with a process thatprovides fast reroute of a packet that may be forwarded on one of aplurality of equal cost multipath routes through a network as explainedherein that when performed (e.g. when executing) on the processor,operates as explained herein within the computerized device to performall of the method embodiments and operations explained herein asembodiments of the invention. Thus any computerized device that performsor is programmed to perform up processing explained herein is anembodiment of the invention.

Other arrangements of embodiments of the invention that are disclosedherein include software programs to perform the method embodiment stepsand operations summarized above and disclosed in detail below. Moreparticularly, a computer program product is one embodiment that has acomputer-readable medium including computer program logic encodedthereon that when performed in a computerized device provides associatedoperations providing fast reroute of a packet that may be forwarded onone of a plurality of equal cost multipath routes through a network asexplained herein. The computer program logic, when executed on at leastone processor with a computing system, causes the processor to performthe operations (e.g., the methods) indicated herein as embodiments ofthe invention. Such arrangements of the invention are typically providedas software, code and/or other data structures arranged or encoded on acomputer readable medium such as an optical medium (e.g., CD-ROM),floppy or hard disk or other a medium such as firmware or microcode inone or more ROM or RAM or PROM chips or as an Application SpecificIntegrated Circuit (ASIC) or as downloadable software images in one ormore modules, shared libraries, etc. The software or firmware or othersuch configurations can be installed onto a computerized device to causeone or more processors in the computerized device to perform thetechniques explained herein as embodiments of the invention. Softwareprocesses that operate in a collection of computerized devices, such asin a group of data communications devices or other entities can alsoprovide the system of the invention. The system of the invention can bedistributed between many software processes on several datacommunications devices, or all processes could run on a small set ofdedicated computers, or on one computer alone.

It is to be understood that the embodiments of the invention can beembodied strictly as a software program, as software and hardware, or ashardware and/or circuitry alone, such as within a data communicationsdevice. The features of the invention, as explained herein, may beemployed in data communications devices and/or software systems for suchdevices such as those manufactured by Avaya, Inc. of Lincroft, N.J.

Note that each of the different features, techniques, configurations,etc. discussed in this disclosure can be executed independently or incombination. Accordingly, the present invention can be embodied andviewed in many different ways.

Also, note that this summary section herein does not specify everyembodiment and/or incrementally novel aspect of the present disclosureor claimed invention. Instead, this summary only provides a preliminarydiscussion of different embodiments and corresponding points of noveltyover conventional techniques. For additional details, elements, and/orpossible perspectives (permutations) of the invention, the reader isdirected to the Detailed Description section and corresponding figuresof the present disclosure as further discussed below.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing will be apparent from the following more particulardescription of preferred embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention.

FIG. 1 is a functional block diagram showing a first example oforganizing a cluster of nodes;

FIG. 2 is a functional block diagram showing another example oforganizing a cluster of nodes;

FIG. 3 is a functional block diagram showing another example oforganizing a cluster of nodes;

FIG. 4 is a functional block diagram showing another example oforganizing a cluster of nodes;

FIG. 5 is a functional block diagram showing another example oforganizing a cluster of nodes;

FIG. 6 is a functional block diagram showing another example oforganizing a cluster of nodes;

FIG. 7 is a functional block diagram of an example communicationnetwork;

FIG. 8 is a functional block diagram of an example network element;

FIG. 9 is a functional block diagram of an example line card that may beused in a network element such as the network element of FIG. 8;

FIG. 10 is a functional block diagram of an example port database thatmay be used in a line card such as the line card of FIG. 9;

FIG. 11 is a functional block diagram of an example cluster of networkelements showing the flow of port state information between thecomponents of the datapath within the node cluster;

FIG. 12 illustrates an example computer system architecture for anetwork element that operates in accordance with embodiments of theinvention;

FIG. 13 comprises a flow diagram of a method for providing fast rerouteof a packet for standalone ports that may be forwarded on one of aplurality of equal cost multipath routes through a network in accordancewith embodiments of the invention; and

FIG. 14 comprises a flow diagram of a method for providing fast rerouteof a packet for multilink trunk ports that may be forwarded on one of aplurality of equal cost multipath routes through a network in accordancein accordance with embodiments of the invention.

DETAILED DESCRIPTION

Over time, the manner in which network elements handle data has evolved.For example, two or more physical links may extend between a group ofnetwork elements and be used collectively as a MLT or LAG. FIG. 1 showsan example of two network elements (network element 1 and networkelement 2) connected by multiple links 24 a-d that have been grouped toform a multi-link trunk 22. In particularly, each of the links 24 a-d inthe MLT 22 may be used by either of the network elements to forward datato the other. Thus, if network element 1 has data (e.g. a frame/packet)to send to network element 2, network element 1 may select one of thelinks 24 a-24 d from the MLT 22 and transmit the packet over that linkto network element 2.

FIG. 2 shows another example way in which network elements may beinterconnected. Specifically, in this example network element 1 andnetwork element 2 are interconnected by an inter-switch trunk (IST) 26which may be a single link or itself may be a multi-link trunk. When thelinks of a multilink trunk are physically connected to two differentnetwork elements, the MLT is called a Split Multi-Link Trunk (SMLT).Network elements 1 and 2 may each have one or more links that connectsto network element 3, which may be grouped together to form a SMLT 23.Thus, if network element 1 has data (e.g. a frame/packet) to send tonetwork element 3, network element 1 may either select one of the SMLTlinks connected to it or may transmit the packet on one of the linksassociated with the Inter-Switch Trunk 26 to enable the network element2 to forward the data on one of its links associated with the SMLT tonetwork element 3.

FIG. 3 shows another example in which network element 1 does not haveany links connected to the SMLT 23, but is connected by ISTs 25 and 26to two other network elements (network element 2 and network element 3)that do have ports connected to the links associated with the SMLT. Inthis scenario, if network element 1 has data to send on the SMLT, itwill select one of the IST links (note that each IST link may itself bea SMLT) and forward the data on to either network element 2 or 3. TheISTs may be physical and extend directly between two network elements ormay be logical and extend on tunnels through one or more intermediatenetwork elements.

FIG. 4 shows another example in which network element 1 alsoparticipates in the SMLT 23. In this instance, if network element 1 hasdata to send, it may forward the data on one of its links associatedwith the SMLT 23 or may forward the data on one of the links associatedwith one of the ISTs 25 or 26 to enable the data to be forwarded on theSMLT 23.

FIGS. 5 and 6 show another way of interconnecting network elements in asquare SMLT arrangement. In the arrangement shown in FIG. 5, fournetwork elements are interconnected via ISTs 25-28 in a squarearrangement, and in FIG. 6 the four network elements are interconnectedvia ISTs 25-28 in a meshed arrangement. The ISTs may be physical andextend directly between two network elements or may be logical andextend on tunnels through one or more intermediate network elements.

Although several examples of ways in which network devices may beinterconnected have been shown, there are other ways to interconnect acluster of network elements as well and this example set ofinterconnection architectures is not intended to be exhaustive. Thus,these examples were merely intended to provide a representative exampleof a few ways of interconnecting network elements. A group of networkelements will be referred to herein as a cluster.

FIG. 7 shows an example communication network 10 in which subscribers 12connect to an edge switch 14. The edge switch 14 connects to coreswitches 16 which forward data through the network on links 18. Each ofthese switches may be a physical rouswitchter or may be multiple devicesconnected together to operate as a cluster. Each of the links 18 may bea MLT or, where the router/switch is implemented as multiple physicaldevices, may be a SMLT. From a network routing standpoint, there may bemultiple ways for a packet to traverse the network. For example, in FIG.7 the edge switch A may be able to transmit a packet to edge switch Bthrough core switches C and D or, alternatively, may be able to transmitthe packet through core switches E and F. A network layer routingprotocol may be used to determine the path to be used for transmissionof the packet.

As noted above, depending on the manner in which the network elementsare interconnected, there may be many ways for the network element toforward a frame/packet to enable the frame/packet to reach itsdestination. As used herein, the term “cluster” is used to refer to oneor more nodes providing node-level resiliency at the network level.Thus, in FIG. 1, network element 1 would be a cluster; in FIG. 2 networkelements 1 and 2 would be a cluster, and in FIGS. 3 and 4 networkelements 1, 2, and 3 would be a cluster and in FIGS. 5 and 6 networkelements 1-4 would be a cluster. As noted above there are other ways oforganizing nodes within a cluster.

Logical connections between the cluster nodes are referred to herein asInter-Switch Trunks (ISTs). ISTs may be physical links that extend fromone network element to a neighboring network element in the cluster, ormay be logical links that tunnel through one or more intermediatenetwork elements within the cluster. The node that receives a packetfrom a non-IST port will be referred to as a local node. All other nodeswithin the cluster are referred to as remote nodes with respect to thereceived packet.

Two or more links may be grouped to form a Multi-Link Trunk (MLT). EachMLT will be assigned a MLT group ID (MLT-ID), which is a global valuewithin the cluster and unique across the cluster nodes. An MLT with allits port members only on one node is referred to as a normal MLT group.An MLT group where its port members are on two or more nodes is referredto as a Split MLT or SMLT group.

When a logical port is implemented as a MLT or SMLT, there are actuallymultiple physical ports that are capable of forwarding a packet to itsnext hop on the network. Accordingly, if one of the ports of a MLT/SMLTfails, it would be advantageous to cause the packet to be forwarded onone of the remaining ports so that the packet can traverse the networkrather than being dropped. Likewise, rather than designate a primary andbackup port for each port in the MLT/SMLT, it would be advantageous toload share the packets across the remaining ports of the MLT/SMLT sothat the packets may be distributed across the remaining ports that areUP. According to an embodiment, this process is implemented in hardwareso that the fastpath (dataplane) can automatically accommodateindividual and multiple port failures and automatically redirect packettraffic across the remaining ports in an equitable manner.

FIG. 8 shows a functional block diagram of an example network element 20which may be used as any of the network elements shown in any of FIGS.1-6. In the example shown in FIG. 8, the network element includes acontrol plane 31 and a data plane 32. The control plane has one or moreCPUs 34 and generally run control processes such as routing processes,management processes, etc. The control plane programs the data plane toinstruct the data plane how to forward data on the network.

The data plane 32 may be constructed using many different architecturesand the example shown in FIG. 8 is only one example of one sucharchitecture. In the example shown in FIG. 8, the data plane includes aplurality of line cards 36 each of which implements multiple physicalports which connect to links in the network. The line cards in thisembodiment are interconnected by a switch fabric 40, although in otherembodiments the line cards may be directly interconnected and performswitching functions in a distributed manner.

As shown in FIG. 9, each line card 36 includes a plurality of ports 38which physically connect to the links on the network. The line card alsoincludes one or more functional units 42 that process packets receivedfrom the attached ports. As used herein, the functional unit thatprocesses packets from attached ports in both ingress and egressdirections, and makes forwarding decisions, is referred to as aForwarding Datapath Unit or FDU 42. The line card may also include a CPU44 that interacts with the control plane to enable the control plane toprogram instructions into the FDU 42 and optionally other components onthe line card so that the FDU 42 will handle data appropriately on thenetwork. The CPU 44 also periodically checks the status of the FDU 42and other components of the line card to detect when a failure occurs.

Each FDU 42 maintains a port state database 46. This port state database46 maintains the physical link states and connection states for itslocal as well as all remote ports. As shown in FIG. 10, the port statedatabase 46 includes two tables—a local port data table 48 and a remoteport data table 50. The local port data table 48 maintains the portstates belonging to the local node, and the remote port data table 50maintains the port states belonging to the remote nodes within thecluster. In the case of MLT groups, the FDU keeps the MLT port memberson the local node in the local table, and the port members on all otherremote nodes in the remote table.

When the FDU receives a packet, it is required to find a port within theMLT (or SMLT) that is UP to forward the packet on toward its destinationon the network. As noted above, where all the ports on the MLT arelocal, the FDU will need to determine which of the local ports is in theUP state so that it does not attempt to forward the packet over a portthat is DOWN. Likewise, where the ports associated with the MLT are notall local (e.g. SMLT), the FDU will need to select a port on a separatephysical network element that is associated with the SMLT and has an UPstate.

According to an embodiment, each FDU maintains a port state database 46that it uses to maintain the state of each port within the cluster. Thedatabase maintains the physical link states and connection states forits local as well as all remote ports. The database includes twotables—namely a local table 48 and remote table 50. The local tablemaintains the port states belonging to all FDUs on the local node, andthe remote table maintains the port states of all ports on all remotenodes within the cluster. In the case of MLT groups, the FDU keeps thestate of the MLT port members that are on the local node within thelocal table, and keeps the state of the MLT port members that are on allother remote nodes in the remote table. The local table also maintainsthe state of all IST ports. When a packet is received, the FDU will usethe port state database to determine a port for the packet that is UPand forward the packet to that port to be output on the network.

Since the port state database 46 is used by the FDU 42 to makeforwarding decisions, it is important to keep the port state tableupdated, so that it contains current information about the state of eachof the ports. Since each line card has one or more FDU, each FDU (ineach line card) is required to synchronize with the FDUs in all otherline cards within the local network element as well as with all otherFDUs in other network elements within the cluster.

In one embodiment, each line card maintains heartbeat timers. Each timea particular one of the heartbeat timers expires, a heartbeat engine 54generates a heartbeat packet and sends the heartbeat packet to the localFDU 42 on that line card. The heartbeat packet carries the localphysical link status of all ports on the line card to inform the localFDU of the state of the ports on that line card. The packet indicatesthe Global Port ID (GPID) and a network element ID. The FDU uses thisstate to update its local port state database. The FDU will also forwardthe packet to all of the other FDUs within the local node, as well as toall other FDUs on other nodes within the cluster. Each FDU uses the portstate carried by the packet to update its port state database.

In addition to maintaining a timer associated with collecting/reportingits own port state information, each line card/FDU will also maintain aset of timers associated with all other FDUs within the local node andall other FDUs on other nodes within the cluster. Each FDU expects toreceive periodic heartbeat packets from every other local and remoteFDU. Thus, a local reception timer is maintained per FDU (for each FDUon the local network element as well as for each FDU on each remotenetwork element within the cluster). A FDU failure (local or remote) isdetected if the corresponding reception timer expires. Where a heartbeatpacket is not received before expiration of the reception timer, eachport associated with the FDU will be set to DOWN so that packets are notsent to ports associated with that FDU until it is restored.

The heartbeat packets allow the FDUs to convey state information to eachother and allow each FDU to know the state of all ports in thedataplane. As described below, this allows the dataplane toautomatically adjust to port failures so that data may be redirected toports that are UP and away from ports that are Down. All this happenswithout intervention from the control plane and, hence, the controlplane is not notified of a failure of a particular port/line card. Toenable the control plane to learn of dataplane failures, themanagement/control processor 44 periodically injects and extractsheartbeat packets into and out of its local FDU 42. Each injectedheartbeat packet completely loops through the target FDU and associatedports and then is extracted back to the processor. The managementheartbeat packet traverses all functional blocks in both ingress andegress datapaths. Each time the control processor injects a managementheartbeat packet of this nature, it kicks off its correspondingreception timer. The control processor detects a failure of the linecard if the reception timer expires. The processor uses this informationto set a system alarm which will be conveyed to the control plane 30.The control plane may thus learn about a data plane failure. However,since the dataplane has a self-healing mechanism to accommodate portfailures and redirect traffic accordingly, the control plane is notrequired to be involved in redirecting traffic and, hence, notificationof the control plane of the failure is not critical to restoration oftraffic through the network element.

Heartbeat packets are also used by each FDU to determine the state ofits ports. In one embodiment, each FDU maintains a pair of timers perattached port that is configured in a logical/virtual connection. One ofthe timers is used to generate heartbeat packets to be sent over theconnection. The other timer (reception timer) is used to detectconnection failure. This timer expires if the heartbeat packet from theother endpoint of the connection is not received in time. The FDUupdates its port state table with the arrival of heartbeat packets andreception timer expirations.

Each FDU on each line card maintains its own port state table 46. Thistable maintains the physical link states and connection states for itslocal ports as well as all remote ports of all FDUs in the cluster. TheFDU uses the received heartbeat packets and timer expiration messages(due to connection time-out or remote FDU failure) to update the table.The table is partitioned into two segments: port states belonging tolocal node and port states belonging to the remote nodes. The port statetable also maintains MLT and SMLT group information. The port statetable is used by the forwarding logic to perform fast reroute asexplained in greater detail below.

FIG. 11 shows dissemination of the port state packet within a cluster offour nodes, in which the dark arrows represents the flow of the portstate packet to all FDUs in the cluster. As shown in this figure, packet1 will be generated containing the state of each port associated with aparticular FDU. This packet is shown with reference numeral 1 in the topleft line card of the top left network element. This packet will bepassed to the FDU so that the FDU can update its port state database toreflect the current status of its ports. The packet will then be passedto each of the other FDUs within the local node (arrows 2). In oneembodiment this may be implemented by causing the packet to be broadcastby the switch fabric to all other FDUs within the local node. The packetwill also be forwarded to other nodes within the cluster (arrows 3) sothat the state of the port may be distributed (arrows 4) to each FDUassociated with each node of the cluster. Whenever a FDU receives apacket containing port state information, it will use the information toupdate its own port state database. This enables the port state databaseof all FDUs in the cluster to be synchronized.

There may be several network elements within a cluster, multiple FDUswithin a network element, and multiple ports supported by each FDU. Toenable each node to keep track of which FDUs have provided statepackets, and to correlate particular port state packets with particularFDUs, a numbering scheme may be implemented. Preferably the numberingscheme is implemented to be cluster wide unique so that each FDU withinthe cluster may be uniquely identified. In one embodiment, the portstate packet carries information about each of its ports. The packetwill specify the source node ID and the Global Port ID (GPID). TheGlobal Port ID is the globally unique identifier (globally unique withina node) that enables the port to be uniquely identified within the portdatabase.

The previous messages described how the FDUs exchanged messages toenable port state to be synchronized between ports in the datapath. Inoperation, this port state information will enable the FDUs to select anavailable port for a particular data packet with confidence that theselected port is UP. As ports go Down, the FDUs in the cluster will stopselecting those ports and will instead select alternate ports within theMLT/SMLT associated with the down port to be used to handle the packet.Accordingly, the datapath is able to automatically accommodate portfailures, line card failures, etc., to reroute packets to availablealternate ports without involvement of the control plane. Hence,rerouting of packets may be done quickly within a network element andbetween clusters of network elements in under 10 ms.

When a FDU receives a data packet it will read the port ID, MLT-ID, andhash function, and pass the these values to the port state database. Theport state database will search first for a local port that isassociated with the MLT-ID and which is UP, and then send for a remoteport that is associated with the MLT and is UP. In one embodiment, theport state table is designed to offload port selection processing fromthe FDU. In this embodiment, the FDU passes a request for a port to theport state table and the port state table intelligently implements therequest to return a port that is guaranteed to be UP, which is part ofthe MLT/SMLT, and with preference to use of local ports over remoteports. Additionally, where the port is on a remote node, the port statetable will check to find an IST port that is UP over which the FDU canforward the packet to the remote node, so that the remote node canforward the packet on the remote port. Thus, the port state table notonly determines whether there is an available remote port, but alsowhether there is an available IST port that the FDU can use to pass thepacket to the remote node for forwarding over the remote port.

FIG. 10 shows an embodiment that may be used to offload port selectionfrom the FDU. In the embodiment shown in FIG. 10, the port databaseincludes database control logic 56 configured to receive requests forport selection from the FDU and return an available port if one exists.The port database may need to make multiple database accessoperations/calls to the local and remote port tables to determine whichport should be returned in response to the port selection request. Thedatabase control logic controls execution of this process, optionallyunder the control of the FDU, to automate the process of selecting aport.

The database control logic may be implemented in hardware and performdata accesses in the local and remote tables which are also implementedin hardware. As ports fail, the status (UP/Down) of the port will bereflected in the port state table. The FDU will perform a port accessoperation via the database control logic into the port state tablewhenever the FDB lookup returns a destination that is part of anMLT/SMLT group. Accordingly, rather than having the FDU determine theport from the FDB (which is updated by the control pane and, hence, isrelatively slow), the FDU uses the FDB to determine the receiver andthen separately determines the port to be used to reach the receiverusing the hardware-implemented port database. This enables the port tobe determined dynamically based on the current state of the ports andthe MLT group ID, so that an available port from the group of associated(MLT) ports can be selected for the packet. This enables the networkdevice to accommodate multiple failures (multiple port/link failures)and quickly adapt by re-routing the packets away from ports that aredown to ports that are guaranteed to be UP within the MLT. Since portfailure notifications span multiple network devices within the cluster,the FDU may forward a packet to another port on a different node so thatport selection within and between network devices may be implemented ina similar manner. This enables not only port selection from within a MLThaving only local ports, but enables port selection to be implementedbetween ports implemented on separate nodes within a cluster so thatport selection within a SMLT may be dynamically implemented.Additionally, since the nodes are able to select from between all otherports associated with the MLT/SMLT, traffic from the port that is downmay be spread/distributed across the remaining ports of the MLT/SMLTrather than being shifted entirely to a particular alternate port.Likewise, multiple port failures and combinations of port failures maybe accommodated without disrupting packet forwarding through the nodecluster, since whenever a packet is received the port state databasewill be able to look for any available port that is UP and return thevalue of any available port for use by the FDUs.

There are times where the network may have redundancy at the networklayer (layer 3) which may enable redundant routes on the network to bebuilt. One such scenario is Equal Cost MultiPath (ECMP) where there aretwo or more equivalent cost routes through the network to a particulardestination. In this scenario, the ingress FDU will use a hash functionto select one of the ECMP routes. The FDU will then use the port tableto determine which port associated with the selected ECMP route is UP.If no port is UP, the process will iterate for each ECMP route to try tofind an available port. Thus, in the ECMP context, if the FDU is notable to select an available port for the selected ECMP route, the FDUwill then select the next ECMP route and perform the unicast portselection process for that ECMP route to attempt to find an availableport from the next available ECMP route. The FDU will process each ECMProute in order or using rehash distribution until an available port islocated. If no port is available the packet will be dropped.

FIG. 12 is a block diagram illustrating example architecture of acomputer is system (FDU) 110 that executes, runs, interprets, operatesor otherwise performs a ECMP fast reroute operating application 140-1and ECMP fast reroute operating process 140-2 suitable for use inexplaining example configurations disclosed herein. As shown in thisexample, the computer system 110 includes an interconnection mechanism111 such as a data bus or other circuitry that couples a memory system112, a processor 113, an input/output interface 114, and acommunications interface 115. The communications interface 115 enablesthe computer system 110 to communicate with other devices (i.e., othercomputers) on a network (not shown).

The memory system 112 is any type of computer readable medium, and inthis example, is encoded with a ECMP fast reroute operating application140-1 as explained herein. The ECMP fast reroute operating application140-1 may be embodied as software code such as data and/or logicinstructions (e.g., code stored in the memory or on another computerreadable medium such as a removable disk) that supports processingfunctionality according to different embodiments described herein.During operation of the computer system 110, the processor 113 accessesthe memory system 112 via the interconnect 111 in order to launch, run,execute, interpret or otherwise perform the logic instructions of a ECMPfast reroute operating application 140-1. Execution of an ECMP fastreroute operating application 140-1 in this manner produces processingfunctionality in the ECMP fast reroute operating process 140-2. In otherwords, the ECMP fast reroute operating process 140-2 represents one ormore portions or runtime instances of a ECMP fast reroute operatingapplication 140-1 (or the entire a ECMP fast reroute operatingapplication 140-1) performing or executing within or upon the processor113 in the computerized device 110 at runtime.

It is noted that example configurations disclosed herein include theECMP fast reroute operating application 140-1 itself (i.e., in the formof un-executed or non-performing logic instructions and/or data). TheECMP fast reroute operating application 140-1 may be stored on acomputer readable medium (such as a floppy disk), hard disk, electronic,magnetic, optical, or other computer readable medium. A ECMP fastreroute operating application 140-1 may also be stored in a memorysystem 112 such as in firmware, read only memory (ROM), or, as in thisexample, as executable code in, for example, Random Access Memory (RAM).In addition to these embodiments, it should also be noted that otherembodiments herein include the execution of an ECMP fast rerouteoperating application 140-1 in the processor 113 as the ECMP fastreroute operating process 140-2. Those skilled in the art willunderstand that the computer system 110 may include other processesand/or software and hardware components, such as an operating system notshown in this example.

During operation, processor 113 of computer system 100 accesses memorysystem 112 via the interconnect 111 in order to launch, run, execute,interpret or otherwise perform the logic instructions of the ECMP fastreroute application 140-1. Execution of ECMP fast reroute application140-1 produces processing functionality in ECMP fast reroute process140-2. In other words, the ECMP fast reroute process 140-2 representsone or more portions of the ECMP fast reroute application 140-1 (or theentire application) performing within or upon the processor 113 in thecomputer system 100.

It should be noted that, in addition to the ECMP fast reroute process140-2, embodiments herein include the ECMP fast reroute application140-1 itself (i.e., the un-executed or non-performing logic instructionsand/or data). The ECMP fast reroute application 140-1 can be stored on acomputer readable medium such as a floppy disk, hard disk, or opticalmedium. The ECMP fast reroute application 140-1 can also be stored in amemory type system such as in firmware, read only memory (ROM), or, asin this example, as executable code within the memory system 112 (e.g.,within Random Access Memory or RAM).

In addition to these embodiments, it should also be noted that otherembodiments herein include the execution of ECMP fast rerouteapplication 140-1 in processor 113 as the ECMP fast reroute process140-2. Those skilled in the art will understand that the computer system100 can include other processes and/or software and hardware components,such as an operating system that controls allocation and use of hardwareresources associated with the computer system 100.

Flow diagrams of particular embodiments of the presently disclosedmethods are depicted in FIGS. 13 and 14. The rectangular elements areherein denoted “processing blocks” and represent computer softwareinstructions or groups of instructions. Alternatively, the processingblocks represent steps performed by functionally equivalent circuitssuch as a digital signal processor circuit or an application specificintegrated circuit (ASIC). The flow diagrams do not depict the syntax ofany particular programming language. Rather, the flow diagramsillustrate the functional information one of ordinary skill in the artrequires to fabricate circuits or to generate computer software toperform the processing required in accordance with the presentinvention. It should be noted that many routine program elements, suchas initialization of loops and variables and the use of temporaryvariables are not shown. It will be appreciated by those of ordinaryskill in the art that unless otherwise indicated herein, the particularsequence of steps described is illustrative only and can be variedwithout departing from the spirit of the invention. Thus, unlessotherwise stated the steps described below are unordered meaning that,when possible, the steps can be performed in any convenient or desirableorder.

Referring now to FIG. 13, a particular embodiment of a method 200 forproviding fast reroute of a packet that may be forwarded on one of aplurality of equal cost multipath routes through a network is shown.Method 200 begins with processing block 202 which discloses receiving aunicast packet by a Forwarding Data Unit (FDU) in a data plane of anetwork element and wherein said unicast packet is routes at L3 andwherein ECMP is enabled for a next hop for said unicast packet.Processing block 204 states selecting an ECMP route for forwarding thepacket to a destination port. As shown in processing block 206 adetermination is made whether the destination port is a stand-alone portor a MLT group. When a packet is received at a FDU, the preferred ECMProute will be determined, e.g. by using a hash function. A destinationport for the ECMP route will then be determined.

Processing block 208 recites performing a lookup in a port state tablemaintained by the FDU to determine an available local port for said ECMProute that is in an UP state for the destination, and if no local portis UP, then performing a lookup in the port state table to determine anavailable remote port that is in an UP state for the selected ECMProute. When the destination port for an ECMP route is a stand-aloneport, the FDU will pass the destination port to the database controllogic to determine whether the standalone port is UP or Down. If thestandalone port is UP, the FDU will forward the packet over that port.

Processing block 210 discloses if no available port is determined forthe selected ECMP route, selecting another ECMP route if another ECMProute is available and repeating said performing the lookup in the portstate table until a port is found for the packet. If the port is down,the FDU picks another ECMP route which resolves to another destinationport and will iterate for each ECMP route until a port is found or allECMP routes are exhausted. Processing block 212 states forwarding saidpacket to said available port using said ECMP route. Processing block214 recites determining there are no more ECMP routes available thendropping said packet.

The method 200 of FIG. 13 details the process when the destination portis a standalone port, while the method shown in FIG. 14 details theprocess when the destination port is a MLT group. Referring now to FIG.14 a particular embodiment a method 300 wherein the destination port isa MLT group is shown. Method 300 begins with processing block 302 whichdiscloses when the destination port is a MLT group, then generating ahash value from selected fields of said packet to determine a MLT portmember. If the destination port associated with a particular ECMP routeis a MLT group, a hash value generated from selected fields of thepacket is used to pick an MLT port member.

Processing block 304 states using the MLT group ID and the hash value todetermine a port member that is in the UP state. The group ID and thehash value are then used to look up the local port state table. If oneof the local ports is UP, the packet will be sent to that port.

Processing block 306 recites determining whether all port members in alocal table are down, and when the all port members are down, thendetermining an MLT port from a remote table. Processing block 308discloses determining an IST that is in the UP state for a port memberselected from the remote table. If all of the port members in the localtable are down, the FDU uses the remote table to check if any remoteport members are UP. If the check is successful, the FDU sends thepacket to the appropriate IST connection. Processing block 310 statesforwarding the packet to the remote port over the IST. If all the portmembers in the remote table are down, then the FDU picks another ECMProute which resolves to another destination port. The FDU then repeatsthe port selection process. If all attempts for each available ECMProute fail, then the packet is discarded.

By way of the above described method sand apparatus, a fast reroute of apacket that may be forwarded on one of a plurality of equal costmultipath routes through a network is provided.

The device(s) or computer systems that integrate with the processor(s)may include, for example, a personal computer(s), workstation(s) (e.g.,Sun, HP), personal digital assistant(s) (PDA(s)), handheld device(s)such as cellular telephone(s), laptop(s), handheld computer(s), oranother device(s) capable of being integrated with a processor(s) thatmay operate as provided herein. Accordingly, the devices provided hereinare not exhaustive and are provided for illustration and not limitation.

References to “a microprocessor” and “a processor”, or “themicroprocessor” and “the processor,” may be understood to include one ormore microprocessors that may communicate in a stand-alone and/or adistributed environment(s), and may thus be configured to communicatevia wired or wireless communications with other processors, where suchone or more processor may be configured to operate on one or moreprocessor-controlled devices that may be similar or different devices.Use of such “microprocessor” or “processor” terminology may thus also beunderstood to include a central processing unit, an arithmetic logicunit, an application-specific integrated circuit (IC), and/or a taskengine, with such examples provided for illustration and not limitation.

Furthermore, references to memory, unless otherwise specified, mayinclude one or more processor-readable and accessible memory elementsand/or components that may be internal to the processor-controlleddevice, external to the processor-controlled device, and/or may beaccessed via a wired or wireless network using a variety ofcommunications protocols, and unless otherwise specified, may bearranged to include a combination of external and internal memorydevices, where such memory may be contiguous and/or partitioned based onthe application. Accordingly, references to a database may be understoodto include one or more memory associations, where such references mayinclude commercially available database products (e.g., SQL, Informix,Oracle) and also proprietary databases, and may also include otherstructures for associating memory such as links, queues, graphs, trees,with such structures provided for illustration and not limitation.

References to a network, unless provided otherwise, may include one ormore intranets and/or the Internet, as well as a virtual network.References herein to microprocessor instructions ormicroprocessor-executable instructions, in accordance with the above,may be understood to include programmable hardware.

Unless otherwise stated, use of the word “substantially” may beconstrued to include a precise relationship, condition, arrangement,orientation, and/or other characteristic, and deviations thereof asunderstood by one of ordinary skill in the art, to the extent that suchdeviations do not materially affect the disclosed methods and systems.

Throughout the entirety of the present disclosure, use of the articles“a” or “an” to modify a noun may be understood to be used forconvenience and to include one, or more than one of the modified noun,unless otherwise specifically stated.

Elements, components, modules, and/or parts thereof that are describedand/or otherwise portrayed through the figures to communicate with, beassociated with, and/or be based on, something else, may be understoodto so communicate, be associated with, and or be based on in a directand/or indirect manner, unless otherwise stipulated herein.

Although the methods and systems have been described relative to aspecific embodiment thereof, they are not so limited. Obviously manymodifications and variations may become apparent in light of the aboveteachings. Many additional changes in the details, materials, andarrangement of parts, herein described and illustrated, may be made bythose skilled in the art.

Having described preferred embodiments of the invention it will nowbecome apparent to those of ordinary skill in the art that otherembodiments incorporating these concepts may be used. Additionally, thesoftware included as part of the invention may be embodied in a computerprogram product that includes a computer useable medium. For example,such a computer usable medium can include a readable memory device, suchas a hard drive device, a CD-ROM, a DVD-ROM, or a computer diskette,having computer readable program code segments stored thereon. Thecomputer readable medium can also include a communications link, eitheroptical, wired, or wireless, having program code segments carriedthereon as digital or analog signals. Accordingly, it is submitted thatthat the invention should not be limited to the described embodimentsbut rather should be limited only by the spirit and scope of theappended claims.

1. A computer-implemented method in which a network element performsoperations providing fast reroute of a packet that may be forwarded onone of a plurality of Equal Cost Multi Path (ECMP) routes through anetwork, the method comprising the steps of: receiving a unicast packetby a Forwarding Data Unit (FDU) in a data plane of a network element,wherein said unicast packet is routed at L3, and wherein ECMP is enabledfor a next hop for said unicast packet; selecting an ECMP route forforwarding the packet to a destination port; performing a lookup in aport state table maintained by the FDU to determine an available localport for said ECMP route that is in an UP state for the destination, andif no local port is UP, then performing a lookup in the port state tableto determine an available remote port that is in an UP state for theselected ECMP route; and if no available port is determined for theselected ECMP route, selecting another ECMP route if another ECMP routeis available and repeating said performing the lookup in the port statetable until a port is found for the packet.
 2. The method of claim 1further comprising forwarding said packet to said available port usingsaid ECMP route.
 3. The method of claim 1 further comprising determiningthere are no more ECMP routes available then dropping said packet. 4.The method of claim 1 wherein said selecting an ECMP route forforwarding the packet to a destination port comprises determiningwhether said destination port is a stand-alone port or a Multi LinkTrunk (MLT) group.
 5. The method of claim 4 wherein when saiddestination port is a MLT group, then generating a hash value fromselected fields of said packet to determine a MLT port member.
 6. Themethod of claim 5 further comprising using said MLT group ID and saidhash value to determine a port member that is in the UP state.
 7. Themethod of claim 6 further comprising determining whether all portmembers in a local table are down, and when said all port members aredown, then determining an MLT port from a remote table.
 8. The method ofclaim 7 further comprising determining an Inter Switch Trunk (IST) thatis in the UP state for a port member selected from said remote table. 9.The method of claim 8 further comprising forwarding said packet to saidremote port over said IST.
 10. A network element comprising: a memory; aprocessor; a communications interface; an interconnection mechanismcoupling the memory, the processor and the communications interface; andwherein the memory is encoded with an application providing fast rerouteof a packet that may be forwarded on one of a plurality of Equal CostMulti Path (ECMP) routes through a network, that when performed on theprocessor, provides a process for processing information, the processcausing the network element to perform the operations of: receiving aunicast packet by a Forwarding Data Unit (FDU) in a data plane of anetwork element, wherein said unicast packet is routed at L3, andwherein ECMP is enabled for a next hop for said unicast packet;selecting an ECMP route for forwarding the packet to a destination port;performing a lookup in a port state table maintained by the FDU todetermine an available local port for said ECMP route that is in an UPstate for the destination, and if no local port is UP, then performing alookup in the port state table to determine an available remote portthat is in an UP state for the selected ECMP route; and if no availableport is determined for the selected ECMP route, selecting another ECMProute if another ECMP route is available and repeating said performingthe lookup in the port state table until a port is found for the packet.11. The network element of claim 10 further comprising the networkelement performing the operation of forwarding said packet to saidavailable port using said ECMP route.
 12. The network element of claim10 further comprising the network element performing the operation ofdetermining there are no more ECMP routes available then dropping saidpacket.
 13. The network element of claim 10 wherein said selecting anECMP route for forwarding the packet to a destination port comprisesdetermining whether said destination port is a stand-alone port or aMulti Link trunk (MLT) group.
 14. The network element of claim 13further comprising instructions wherein when said destination port is aMLT group, then said network element generates a hash value fromselected fields of said packet to determine a MLT port member.
 15. Thenetwork element of claim 14 further comprising the network elementperforming the operation of using said MLT group ID and said hash valueto determine a port member that is in the UP state.
 16. The networkelement of claim 15 further comprising the network element performingthe operation of determining whether all port members in a local tableare down, and when said all port members are down, then determining anMLT port from a remote table.
 17. The network element of claim 16further comprising the network element performing the operation ofdetermining an Inter Switch Trunk (IST) that is in the UP state for aport member selected from said remote table.
 18. The network element ofclaim 17 further comprising the network element performing the operationof forwarding said packet to said remote port over said IST.
 19. Anon-transitory computer readable storage medium having computer readablecode thereon for providing fast reroute of a packet that may beforwarded on one of a plurality of Equal Cost Multi Path (ECMP) routesthrough a network, the medium including instructions in which a networkelement performs operations comprising: receiving a unicast packet by aForwarding Data Unit (FDU) in a data plane of a network element, whereinsaid unicast packet is routed at L3, and wherein ECMP is enabled for anext hop for said unicast packet; selecting an ECMP route for forwardingthe packet to a destination port; performing a lookup in a port statetable maintained by the FDU to determine an available local port forsaid ECMP route that is in an UP state for the destination, and if nolocal port is UP, then performing a lookup in the port state table todetermine an available remote port that is in an UP state for theselected ECMP route; and if no available port is determined for theselected ECMP route, selecting another ECMP route if another ECMP routeis available and repeating said performing the lookup in the port statetable until a port is found for the packet.
 20. The non-transitorycomputer readable storage medium of claim 19 further comprisinginstructions for forwarding said packet to said available port usingsaid ECMP route.